1. Field of the Invention
The present invention relates to a hollow golf club head, and particularly relates to a golf club head having a shape of a wood type or a shape approximating the shape of the wood type.
2. Description of the Related Art
Hollow metal heads are used broadly as wood type golf club heads for drivers or fairway woods. Generally, a wood type hollow golf club head has a face portion for hitting a ball, a crown portion forming the top surface portion of the golf club head, a sole portion forming the bottom surface portion of the golf club head, a side portion forming the toe-side, rear-side and heel-side side surface portions of the golf club head, and a hosel portion. A shaft is inserted into the hosel portion, and fixed thereto by a bonding agent or the like. Incidentally, recently, many golf club heads called utility clubs are commercially available. Various golf club heads similar to the wood type golf club head (that is, having a face portion, a sole portion, a side portion, a crown portion and a hosel portion) are commercially available as a kind of utility golf club head.
An aluminum alloy, stainless steel or a titanium alloy is used as the metal forming such a hollow golf club head. In recent years, particularly a titanium alloy is used broadly.
When a hollow golf club head is increased in volume, its sweet spot can be expanded. In order to prevent the golf club head from increasing in weight with the increase of the volume thereof, it is considered that fiber reinforced plastic whose specific gravity is smaller than that of the metal is adopted as the constituent material of the golf club head. In this case, the face surface for hitting a ball has to be made of metal in order to secure strength. Therefore, the portion other than the face portion is made of fiber reinforced plastic (FRP).
JP-A-2001-340499 discloses a golf club head in which a crown portion and toe-side and heel-side side portions are made of carbon fiber reinforced thermoplastic (CFRP).
In the golf club head according to JP-A-2001-340499, in which a crown portion and toe-side and heel-side side portions are made of carbon fiber reinforced thermoplastic resin (CFRP), the crown portion and the side portions made of CFRP butt against the circumferential edge of a face portion simply. Markedly great stress is applied to the joint portion between the crown portion and the face portion and the joint portions between the side portions and the face portion when a ball is hit. Particularly, markedly great stress is applied to the joint portion between the face portion and the crown portion. In the golf club head according to JP-A-2001-340499, in which the crown portion and the side portions made of CFRP are butt-joined to the circumferential edge of the face portion simply, there is a possibility that repeated use may result in peeling in the joint portions.